Method for the continuous hot galvanizing of continuously formed elements

ABSTRACT

Method and apparatus for the continuous hot galvanizing of tubing wherein the molten zinc in the zinc furnace and zinc vat are continuously exposed to the atmosphere, and one end of a zinc tube is maintained under a nonoxidizing atmosphere in sealed communication with tubing heating means. The tubing is heated to at least about 1,100* F. prior to entry into the zinc tube.

United States Patent METHOD FOR THE CONTINUOUS HOT GALVANIZING 0F CONTINUOUSLY FORMED ELEMENTS 5 Claims, 3 Drawing Figs.

US. C 117/51, 117/94, 117/102 M, 117/114 A, 117/119, 118/65, 118/405, 148/635 Int. Cl

Field of Search ..l17/94, 114 R, 114A, 114B, l14C,51; 118/404,405

[56] References Cited UNITED STATES PATENTS 3,533,761 10/1970 Pierson 117/51 X 1,605,326 11/1926 Bundy 118/404 X 2,214,108 9/1940 Nichols 118/405 X 2,216,519 10/1940 Quamstrom 117/114 X 2,354,459 7/1944 Harris et a1. ll7/114AUX 2,683,099 7/1954 Hahn 117/1 14 (R) 2,771,056 11/1956 Hess 117/114 (A) X 2,876,132 3/1959 Worden et a1. 117/94 X 3,259,148 7/1966 Krengelet al 117/114( A) X 3,479,210 11/1969 Ross 117/114(A) Primary Examiner-Alfred L. Leavitt Assistant Examiner-J R, Batten, Jr. Attorney- Dressler, Goldsmith, Clement and Gordon ABSTRACT: Method and apparatus for the continuous hot galvanizing of tubing wherein the molten zinc in the zinc furnace and zinc vat are continuously exposed to the atmosphere, and one end of a zinc tube is maintained under a nonoxidizing atmosphere in sealed communication with tubing heating means. The tubing is heated to at least about 1,l00 F. prior to entry into the zinc tube.

METHOD FOR THE CONTINUOUS HOT GALVANIZING OF CONTINUOUSLY FORMED ELEMENTS There are a number of methods presently being used for making galvanized continuously formed elements, such as ferrous tubing intended for use as electrical conduit. One such method comprises the forming of tubing, the cutting of it into sections and then the dipping of the sections into tanks wherein a zinc coating is electrically deposited.

Other methods comprise the continuous forming of tubing and the continuous galvanizing of the formed tubing by passing the tubing through a molten zinc container where a zinc coating is applied to the tubing. Thereafter, the galvanized tubing is cooled and cut into sections. In one such continuous method the heated zinc vat and a zinc container are placed and maintained under a nonoxidizing atmosphere. This method requires careful sealing, a large difficulty movable enclosure cover for the entire furnace and presents obstacles to ready and quick access to the interior of the zinc vat, zinc container and furnace for maintenance and the like. Further, because a large area must be placed under a nonoxidizing atmosphere, if sealing conditions are not very carefully maintained, large quantities of nonoxidizing gases are lost. Also, each time it is necessary to gain access to anything inside of the sealed enclosure, which occurs all too frequently, a large quantity of gas must be wasted and then replenished. These circumstances, and others, make the utilization of such a method, for example as illustrated in Krengel et al. Pat. No. 3,1 22,1 14, less than completely desirable.

Another continuous galvanizing method used has employed a completely open-to-the atmosphere zinc vat and zinc coating container. Omitting the nonoxidizing atmosphere and the attendant disadvantages, however, has frequently resulted in undesirably high zinc losses due to oxidation.

In accordance with the invention herein, a continuous galvanizing system is provided which both reduces the zinc loss of open systems to a nominal amount and eliminates the complex structure and gas losses of the sealed enclosure system. To that end, the invention provides a zinc vat which is always open to the atmosphere and a means for maintaining a nonoxidizing atmosphere only at the point which has been found to be the most critical in terms of oxidation in the zinc furnace. Nonoxidizing gas losses therefore are minimal and the zinc losses are nominal, resulting in a highly economical and efficient galvanizing system.

Further, in accordance with this invention, the continuously formed tubing to be galvanized is maintained at a temperature substantially higher than in the open-to-the atmosphere system from the time it is first heated until it enters the zinc coating tube. This then enables the tubing itself to add heat to the zinc in the zinc coating tube, permitting lower temperatures to be used in the zinc furnace and zinc vat, prolonging the lives of those elements, and facilitating higher line speeds. Because of the increased temperature of the tubing itself, better alloying between the tubing and zinc is accomplished. Also because the temperature of the tubing itself can be maintained at a higher temperature, the coated tubing itself is more stress relieved, giving it a more desirable and uniform external surface appearance and better bending characteristics. That is quite important when it is understood that most of the tubing made by the type of continuous galvanizing processes referred to is used for electrical conduit, much of which is bent when ultimately used. Yet another benefit of the higher temperatures at which the heated tubing can be maintained is in the improved oxide coating formed on the internal surface of the tubing, the texture and quality of which coating permits holding of the galvanized tubing prior to internal painting for much longer periods. In hot, humid weather as much as a days holding period frequently produces internal rusting, flaking and the like, requiring internal cleaning before painting, a timeconsuming and expensive procedure which is minimized when the principles of this invention are practiced.

Thus, in a preferred embodiment of this invention, tubing is formed from strip stock in conventional fashion, is passed through an acid bath, is wiped and then enters an area in which a nonoxidizing atmosphere is maintained. An induction heating coil surrounds a portion of that area in which the tubing temperature is raised to about l,100 F. The tubing then continues to pass through that area to a galvanizing station whereat a zinc tube is continuously fed with an excess of zinc by a zinc pump. The zinc tube defines concentric ports at each end through one of which the uncoated tubing enters and through the other of which the galvanized tubing leaves.

At the inlet end a gas pipe is disposed. The gas pipe sealingly intercommunicates with the heating station at one side and with the inlet port of zinc tube at the other side. The bottom of the gas tube extends below the surface of the zinc in the zinc vat, thereby forming a small chamber above the zinc vat in which the nonoxidizing atmosphere is maintained. The zinc overflow from the inlet port reenters the zinc vat within the chamber.

Although the zinc vat and furnace are open to the atmosphere, it has been found that as much as more than percent of the zinc losses encountered with a zinc vat completely exposed to the atmosphere is avoided, and a very substantial reduction is made in the consumption of nonoxidizing gas, as compared to the use of a sealed enclosure type of system typified by the aforementioned patent.

Further objects and advantages of this invention will become apparent from the following description and drawings, of which:

FIG. 1 is a schematic showing of a preferred embodiment of this invention;

FIG. 2 is a more detailed view of a portion of FIG. I;

FIG. 3 is a perspective and more detailed view of the zinc tube and pump assembly of FIG. 2.

Referring first to FIG. 1, a continuously formed element, such as ferrous tubing T has already been formed from strip stock by conventional and known continuous strip forming and welding procedures. The formed tubing T is then appropriately cleaned and moved by known driving means from the forming and cleaning stations to an acid bath 10 where the external surface is treated in preparation for galvanizing. In many prior art processes it was necessary next to flux the surface of tubing T, at substantial flux expense and with resultant corrosion of downstream equipment. However, in accordance with this invention such fluxing is unnecessary. Therefore, after the acid treatment in acid bath 10 tubing T next passes to an acid resistant wiper 12 where excess acid is removed from the surface of the tubing. Wiper 12 is preferably made of gum rubber which wipingly surrounds tubing T and which is sealingly connected to the members forming the area in which the nonoxidizing atmosphere is maintained. It therefore serves both as a wiping and sealing means.

A nonoxidizing atmosphere, such as an inert nitrogen atmosphere, is provided by a compressed gas source 14 from which gas is metered under pressure and at a suitable rate through gas conduits l6 and 18. Gas conduits l6 and I8 feed gas to opposite sides of a heating station 20. Heating station 20 comprises a heating tube 26, preferably formed of a high-temperature resistant ceramic, which tube 26 is surrounded by a heater, such as an induction heating coil 32. Heating tube 26 is sealingly joined to aligning boxes 24 and 28 each of which internally mounts a pair of opposed rollers (not shown) to support and position the tubing T as it passes therethrough and through tube 26. Each of the aligning boxes 24 and 28 is sealingly connected to a pipe 22 and 30 respectively in which the inert atmosphere is maintained and to which gas is supplied by conduits 16 and 18. Pipes 22 and 30 and aligning boxes 24 and 28 are preferably temperature and corrosion resistant and are formed of materials such as fiberglass, polyvinyl chloride or suitably corrosion-resistant steel.

The tubing T is preferably heated to at least about 1,100 F. as it passes through heating tube 26, and most preferably to a temperature of at least about l,l50 F. Because, as will appear, the volume of the inert atmosphere is quite small as compared to known systems, and because fluxing is unnecessary,

zinc coating tube is reduced substantially, the tubing thus entering the galvanizing station at a much higher surface temperature than in prior art processes. Indeed, it enters the galvanizing station at a temperature greater than the temperature of the molten zinc thereby permitting operation of the furnace at a lower temperature and resulting in many of the other advantages referred to herein.

After the tubing T is heated it passes through aligning box 28, through pipe 30 and into gas pipe 34. Gas pipe 34 is sealingly connected to pipe 30 as by suitable flanging and gasketing at the entry end. Gas pipe 34 defines a gas chamber 36 above the level of the zinc in zinc vat 38. Zinc vat 38 is surrounded by a furnace 40 which maintains the zinc in the elongate vat 38 in a molten condition and desirably at a temperature of about 850 F. This temperature may be as much as 30 to 50 F. lower than in completely open prior art systems, resulting in longer furnace and zinc vat lives. As stated, this, in large measure is due to the fact that the temperature of the tubing entering zinc tube 42 is higher than the temperature of the zinc in the vat 38, thereby adding heat to the zinc, rather than reducing the zinc temperature as was frequently the case in prior art processes.

The gas pipe 34 projects downwardly at its lower end 44 into the molten zinc Z a distance sufficient to preclude the passage of gas into the body of the zinc 2, thereby to avoid loss of gas from chamber 36 into the zinc vat.

The outlet side of the gas pipe 34 is suitably sealingly connected as by flanging to zinc tube 42. The outlet from pipe 34 is concentric with the inlet port 46 in the zinc tube. The inlet port 46 is slightly greater in diameter than the outside diameter of tubing T, so that there is a constant overflow of zinc therethrough, into chamber 36 for return to the main body of molten zinc Z.

The level of the molten zinc in zinc tube 42 is maintained above tubing T as it passes therethrough by a zinc pump as sembly 48. This assembly includes a motor 50 suitably drivingly connected to an impeller shaft 52 terminating in a housing 54 which rotatably supports an impeller 56 and which provides an outlet port adjacent a riser 58. Riser 58 consists of one or more sealingly interconnected pipe sections which feed the zinc tube from its bottom (see FIG. 3). The impeller is rotated by motor 50 at a speed sufficient to provide enough zinc to zinc tube 42 to maintain the level of the zinc above the top of tubing T.

Zinc tube 42 defines an outlet port 60 through which the galvanized tubing exits, and through which an excess of zinc also flows for return to zinc vat 38. Although the exit end of the zinc tube 42 is open to the ambient atmosphere, as is the zinc vat, the zinc loss encountered due to oxidation has been found to be nominal. The skimmings due to oxidation of the zinc, as well as those resulting from other causes are reduced very substantially as compared to prior art processes which are open to the ambient atmosphere.

After the galvanized tubing T leaves outlet port 60, it passes through a wiping means such as a blow bell 62 whereat atmospheric air is directed at an angle against the tubing around its entire periphery, blowing the excess zinc carried by the tubing T out of the zinc tube 42 back into the vat 38. Thereafter the tubing passes to a cooling tank 64 containing a coolant such as water and is further processed in a known and conventional fashion. Suitable well-known means 74 for driving the tubing through the zinc tube and the other stations are provided.

As may be seen from the drawings the pipe sections, aligning boxes, gas pipe and zinc tube are sealingly intercom nected by pairs of flange elements or the like, which are suitably gasketed. The entry and exit ports of the zinc tube are closed by apertured plates which may be interchanged to accommodate tubing of differing outside diameters (i.e., from about A inch to 2 inches in diameter). Preferably, the zinc tube is provided with a plurality of removable pla tes to provide access to the interior of the tube for inspection and mamtenance. Although continuously formed ferrous tubing has been primarily referred to herein in connection with the description of the presently preferred embodiment, other continuously formed elements such as channels and the like may also be so treated.

Tubing produced in accordance with this invention has a strongly alloyed zinc coating and a smooth external surface, notably free of circumferential stress marks. It may be bent without wrinkling or other surface disturbance and is frequently much easier to bend than tubing made by conventional continuous hot galvanizing methods. It also has a uniform dark black oxide internal surface which is more moisture resistant than tubing made in accordance with conventional hot galvanizing processes, which means that internal painting may be delayed longer and that internal painting will provide a more adherent and uniform coating than is conventionally obtained.

What is claimed is:

1. In a method for hot galvanizing continuously formed tubing, the steps comprising continuously moving said formed tubing from the forming station toward a heating station and then in a straight line to a galvanizing station, at said galvanizing station maintaining zinc in an elongate vat in a molten condition, continuously exposing said vat of molten zinc and the surface of the zinc to the ambient atmosphere, continuously filling a horizontal zinc tube spaced above the surface of the molten zinc in said vat at said galvanizing station with molten zinc from said zinc vat by pumping molten zinc from said vat upwardly into said zinc tube, continuously maintaining a nonoxidizing atmosphere in a small chamber in sealing communication with the inlet end of said zinc tube, at said heating station, heating said tubing in a nonoxidizing atmosphere, maintaining said heated tubing in a nonoxidizing atmosphere between said heating means and said small chamber, and passing said tubing in a straight line through said chamber and through said zinc tube wherein said tubing is galvanized, causing said molten zinc continuously to overflow from each end of the tube, at the inlet end into said small chamber and at the other end into said vat and while exposed to the ambient atmosphere.

2. In the method of claim 1 in which said formed tubing is continuously formed ferrous tubing.

3. In the method of claim 2 in which said tubing enters said zinc tube at a temperature higher than the molten zinc in said zinc tube.

4. In the method of claim 3 in which the heating step comprises heating said tubing to a temperature of at least l,l 10 F.

5. In the method of claim 3 in which the heating step comprises heating said tubing to a temperature of at least 1, l 50 F.

* I I! i i Patent No. 3,620,805 Dated November 16, 1971 Inventor(s) Carl Martin It is certified that error appears in the abnve-identified patent and that said Letters Patent are hereby corrected as shown below:

Column a, line 59, "1,110" should be 1,1o0

Signed and sealed this 23rd of May i912.

(SEAL) fittest:

EDWARD E-E.,FLETCHER,JH. Attesting Officer ROBERT COTTSCHALK Com issioner of Patents 

2. In the method of claim 1 in which said formed tubing is continuously formed ferrous tubing.
 3. In the method of claim 2 in which said tubing enters said zinc tube at a temperature higher than the molten zinc in said zinc tube.
 4. In the method of claim 3 in which the heating step comprises heating said tubing to a temperature of at least 1,110* F.
 5. In the method of claim 3 in which the heating step comprises heating said tubing to a temperature of at least 1,150* F. 